The present invention relates to multilayer composites which exhibit special visual effects. In particular the composites exhibit an excellent combination of physical properties including melt strength and impact strength, while providing special visual effects and protection of underlying layers from the detrimental effects of visible and UV light.
Composite articles exhibiting special visual effects, such as colors, or a granite-like or a metallic sparkle appearance, are continually in demand for commercial applications. Such visual effects may often be introduced into a composite by using a suitable special visual effect additive dispersed in a resinous matrix in a single layer of the composite. However, achievement of a special visual effect often requires excessive loading of additive which may detrimentally affect the physical properties of the entire composite. In some examples low melt strength or low impact strength makes the composite difficult to process and unsuitable for its final desired use. Also, the addition of a rubbery impact modifier to the special effects layer, while improving impact strength, adversely affects the desired visual effects. Adequate melt and impact strength may be provided by a separate layer underneath the said special visual effects layer, but materials providing such beneficial properties are often degraded by visible and/or ultraviolet light which may be transmitted through the substantially transparent special visual effects layer. A problem to be solved is to provide multilayer composites which exhibit special visual effects while also maintaining other physical properties such as impact strength, and also while providing protection of underlying layers from degradation by visible and/or ultraviolet light. A further problem to be solved is to provide multilayer composites which are easily manufactured, for example by exhibiting suitable melt strength.
FIG. 1 shows the structure of a multilayer composite that is known in the art. The composite has four layers, an outer or first layer 11 which comprises an acrylic resin; a second layer 12 which is formed from an amorphous acrylonitrile-styrene-acrylate graft copolymer (ASA); a third layer 13 comprising acrylonitrile-butadiene-styrene graft copolymer (ABS); and a fiber-reinforced polymer substrate 14. Material consisting of layers 11, 12 and 13 is marketed in sheet form under the tradename Weather-Pro G by Spartech Corporation, and the sheets of material are thermoformed into boat hulls and other shapes to be the outer skin on fiber reinforced polymer substrate 14. However, special visual effects are difficult to achieve since the ASA layer must serve the purpose of both special effects layer and light-blocking layer.
Commonly owned U.S. Pat. No. 7,135,233 describes multilayer composites comprising an outer layer comprising an acrylic resin, a second layer comprising an acrylonitrile-styrene-acrylate graft copolymer; a third layer comprising a modified ABS graft copolymer; and optionally a fourth layer comprising an acrylic resin. The modified ABS polymer comprises both an acrylonitrile-styrene-acrylate graft copolymer and a polymer modifier that decreases the softening of the ABS on contact with styrene. The requirement for ABS containing resinous modifiers increases the complexity of manufacturing the composite and limits its applications.